Chapter 15 (3) Flashcards
What is the focus of an earthquake?
energy radiates outward in all directions from a central point of an earthquake.
What is the epicenter of an earthquake?
The point on the surface directly above the focus
P-waves (primary)
-Fastest waves
-move in a push-pull motion as waves compress and expand
S-waves (secondary)
-slower than P-waves and arrive second
-move in an up-down motion
Surface waves
-the slowest of the three
-cause the most damage
-move side to side or roll
How do we use seismographs and seismic waves to locate an earthquake epicenter?
The greater the time difference between the p- and s-waves, the farther away the epicenter.
What’s the minimum number of seismographs we need?
3
How does the amount of energy increase with each number on a magnitude scale
Each number on the scale indicates ~32x more energy.
Magnitude scales
measure the amount of energy that is released at the focus.
What is the CURRENT magnitude scale that we use?
Moment Magnitude scale
Modified Mercalli scale.
-intensity scale
-used to gage historical earthquakes that predate seismometers.
What happens when seismic waves travel through soft sediments vs. bedrock?
-Soft sediment will amplify seismic waves and increase damage to structures.
-Bedrock will dampen the seismic waves and decrease the amount of damage
What is liquefaction? How does it happen?
Earthquake vibrations cause loose, water-saturated sediment to turn from relatively stabile ground into mobile fluid.
What is a tsunami?
massive waves set in motion by seismic activity.
What are some “precursors” to earthquakes?
Why are such “precursors” not useful for predicting earthquakes?
-Foreshocks
-Bizarre animal behavior
-Changes in groundwater table.
-Release of radon gas or methane from the ground
-can happen for no reason
